This application investigates the early embryonic events that underlie the development of sensory neurons that innervate the taste system. Specifically, it asks how neurons segregate to gustatory or non-gustatory (somatosensory) modalities. Cranial nerve ganglia that carry taste information arise embryonically from epibranchial placodes and the neural crest. Cell labeling and tissue transplantation techniques will be used to fate map placodes and crest to determine the embryonic origin of gustatory neurons. Gustatory neurons are dependent on brain derived neurotrophic factor (BDNF) for survival. When during development do gustatory neurons require BDNF and what is the source of BDNF required by gustatory neurons? These questions will be addressed using a molecular genetic approach, in which BDNF is selectively deleted from subsets of cranial ganglionic neurons in transgenic mice. The mechanisms involved in cranial nerve development are likely to be broadly involved in many aspects of early sensory system development. My results will lend basic insight into events of normal vertebrate embryogenesis and provide elementary data for the study of neurological defects. [unreadable] [unreadable] [unreadable]